The invention relates to a construction machine having at least one material receiver that is adjustable by means of at least one hydraulic actuator for unloading, with the required feed pressure for the actuator actuation being able to be provided by a hydraulic circuit of the construction machine and with the feed pressure being able to be limited to a limit pressure by means of at least one pressure limiting device.
An example for construction machinery of the category is a dump truck, in particular an articulated dump truck. This machinery serves for earthmoving and has a loading surface in the form of a so-called bed as a material receiver. The bed provided for receiving the load is supported in a tiltable manner at the chassis via one or more hydraulic cylinders to unload the received load by lifting the bed. The required energy for the tilt cylinders is provided by the internal hydraulics of the machine.
To avoid an overload of individual hydraulic components, the hydraulics typically comprise at least one pressure limiting device that limits the system pressure to a maximum pressure level. The predefined maximum pressure level determines the maximum possible tilt force of the actuators for lifting the bed. The dimensioning of the maximum pressure level in practice depends on the required tilt force for lifting the bed with a permitted maximum load. The maximum permitted tilt pressure is consequently permanently set to a predefined fixed value at the control valve and is independent of the current operating state of the machine.
The aforesaid solution can, however, be problematic with an unfavorable weight distribution of the received load on the bed since in this case a higher tilt force can optionally be required to lift the bed that can, however, not be reached due to the pressure limitation. In this case, the hydraulics cannot apply the required power, not even when the current load of the bed does not exceed the permitted upper limit.
The same applies to the practical case that occurs as a rule in which the dump truck reverses to a ramp to unload the loaded material. A slanted position of the construction machine and a displacement of the center of gravity of the load material thereby caused occurs due to the ramp slope. This can equally result in an increase in the required tilt pressure for the unloading procedure. Under certain circumstances the machine position or the vehicle inclination then has to be changed to make an unloading of the bed possible.
European patent EP 2 836 394 takes up this problem and provides as the solution to the problem a switching over of the regular maximum tilt pressure to a second higher maximum pressure when a predefined angle of inclination of the machine is exceeded. An unloading of the material receiver is admittedly hereby made possible with an increased tilt pressure; however, this solution is not very flexible with only two limit values. The teaching of this patent can also not solve the problem that occurs with an disadvantageous load distribution.
The above-described problem can also occur in practice with conventional excavators since here a limit value is also required for the hydraulic pressure for actuating individual actuators to raise the excavator bucket so that under certain circumstances an actuation of the excavator bucket, of the grab, or of another attachment tool or of the excavator arm may also not be possible with a permitted load. Excavators thus also represent construction machinery of the category as part of the invention in which the material receiver is formed by the excavator bucket, by the grab or similar.